1. Field of the Invention
The present invention relates to microwave circuits. More specifically, the present invention relates to switches used to connect signals from two or more microwave channels.
While the present invention is described herein with reference to a particular embodiment for an illustrative application, it is understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teaching provided herein will recognize additional modifications, applications and embodiments within the scope thereof.
2. Description of the Related Art
Microwave switches selectively connect channels in microwave circuits and systems. Two categories of switches pertinent to this invention are coaxial switches and waveguide switches.
Coaxial switches are known to have several limitations. The most severe being power handling capability. The maximum average power that a coaxial switch can handle is typically limited by overheating of the internal switch materials due to RF losses. Conventional designs typically exhibit poor thermal conductivity from the transmission line center conductor. Poor thermal conductivity can lead to excessive heat build-up which can cause the safe operating temperatures of the materials being used to be exceeded resulting in failures.
Further, the peak power is limited by multipacting breakdown. Multipacting breakdown is a resonant radio frequency discharge which is attributable to secondary emissions of electrons from discharging surfaces when a radio frequency field of sufficient magnitude and proper frequency is applied across a gap in a vacuum. Multipacting causes disruption of communications and if not controlled can lead to destruction of the switch.
Many coaxial switches of conventional design are inclined to suffer from multipacting breakdown at low power levels and certain (i.e. L and C) frequency ranges. As a result, many current applications, particularly those of spacecraft systems, are increasingly requiring power handling capabilities beyond those of such conventional coaxial switches.
Coaxial switches are also generally more mechanically complex than other designs. As a result, many switch configurations, though realizable, are difficult and costly to implement in a coaxial design.
Waveguide switches do not have the mechanical complexity or the power limitations of the coaxial switches. However, these switches are generally much larger and heavier than coax switches for C band and lower frequencies. Thus, current waveguide switches are generally not acceptable for use in many spacecraft applications.
There is therefore a recognized need in the art for a high power handling, small, lightweight microwave switch suitable for spacecraft systems and other applications demanding a high ratio of power handling capability to size and weight.